Stern drive for boats

ABSTRACT

Two hydraulic cylinders, one on each side of the stern drive and disposed between the tilt housing and the dirigible unit, steer the latter on the axis of the vertical drive shaft. The tilt housing is carried by lateral trunnions rotatable in bearings of the transom mounting on a transverse axis generally passing near the center of the universal joint in the horizontal drive shaft which extends through the transom. A trim adjustment and power tilt cylinder is disposed between the tilt housing and the transom mounting. The dirigible unit is suspended by the vertical drive shaft from an upper gear housing which in turn is removably secured to the tilt housing. The vertical drive shaft is protected from thrust and impact stresses by a steering support tube constituting a part of the dirigible unit and surrounding the shaft within a sleeve of the upper gear housing.

United States Patent Lohse June 10, 1975 1 1 STERN DRIVE FOR BOATSPrimary ExaminerTrygve M. Blix Assislam Examiner-Jesus D. Sotelo {75]lnvemor' lfi Lohse Fond du Attorney, Agent, or FirmAndrus, Sceales,Starke &

Sawall [73] Assignee: Kiekhaefer Aeromarine Motors.

on 57 ABSTRACT [22] Filed: Mar. 29, 1974 [52] U.S. Cl. 115/41 HT; 115/35[51] Int. Cl B63h 5/12 [58] Field of Search 115/34 R, 34 A, 35, 37,115/41 R, 41 HT [56] References Cited UNITED STATES PATENTS 2,961,98811/1960 Wood 115/41 R 2,979,019 4/1961 Leavitt et a1 115/34 R 3.1 36,2826/1964 Alexander, Jr. 115/35 3,181,495 5/1965 Kiekhaefer 115/34 R3,202,125 8/1965 Morse 115/35 3,605,677 9/1971 Bergstedt.... 115/353,654,889 4/1972 Bergstedt 115/35 Two hydraulic cylinders, one on eachside of the stern drive and disposed between the tilt housing and thedirigible unit, steer the latter on the axis of the vertical driveshaft. The tilt housing is carried by lateral trunnions rotatable inbearings of the transom mounting on a transverse axis generally passingnear the center of the universal joint in the horizontal drive shaftwhich extends through the transom. A trim adjustment and power tiltcylinder is disposed between the tilt housing and the transom mounting.The dirigible unit is suspended by the vertical drive shaft from anupper gear housing which in turn is removably secured to the tilthousing. The vertical drive shaft is protected from thrust and impactstresses by a steering support tube constituting a part of the dirigibleunit and surrounding the shaft within a sleeve of the upper gearhousing.

23 Claims, 8 Drawing Figures PATENTEDJUH l 0 m5 888203 I ILL! 1 AC Du CuO PATENTEDJUN 10 I975 wig/A STERN DRIVE FOR BOATS BACKGROUND OF THEINVENTION This invention relates to a stern drive for boats.

Heretofore, stern drives employing a double universal joint providing anextensible horizontal drive shaft through the boat transom have beenconstructed with both the tilt axis and the steering axis passingsubstantially through the center of the effective universal joint.

Such a construction, particularly where it simulates a gimbal ring.requires very heavy expensive parts to withstand the forces involved.

SUMMARY OF THE INVENTION In carrying out the present invention, thesteering axis coincides with the vertical drive shaft axis substantiallyto the rear of the universal joint. and at least some of the samebearing assemblies are utilized for supporting the vertical drive shaftand also the dirigible propulsion unit in the upper gear housing.

The horizontal transverse tilt axis generally passes through or justabove the center of the double universal joint in the horizontal driveshaft and a single trim hydraulic power cylinder is disposed between thetilt housing and the transom.

Thus, the steering and the trim or tilt mechanism are fully operativeindependently of each other with separate parts for each whereby theforces can be taken care of more adequately.

The stern drive is constructed with a parting line that permits themounting plate with the tilt mechanism, horizontal drive shaft andsteering control mechanism to be installed on the transom by the boatmanufacturer, and to which the outer vertical drive shaft assembly andunderwater unit may be readily attached by the customer.

The vertical drive shaft is mounted in roller bearings, the upper ofwhich is operative in the upper gear housing and a lower of which isoperative in the lower unit with the nut at the upper end of the shaftpre-loading the bearings for both the shaft and for steering purposes.Additional needle bearings support the lower unit in the upper gearhousing, and a frictionless hearing is disposed in a generallyhorizontal abutment plane between the lower unit and the upper gearhousing to take the axial pre-loading thrust referred to.

The inboard engine exhaust is conducted through a channel on themounting plate to be discharged rearwardly therefrom through an openingor openings above the level of the anti-cavitation plate.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustratethe preferred embodiment of the invention as presently contemplated bythe inventor.

In the drawings:

FIG. I is a vertical longitudinal section of the stern drive unit shownas attached to the transom of a boat;

FIG. 2 is a vertical transverse section of the drive unit taken on line22 of FIG. coincident of the vertical drive shaft axis;

FIG. 3 is a detail section taken on line 3-3 of FIG. 1 and showing thetilt trunnion and bellows construction;

FIG. 4 is a vertical section of the mounting plate taken on line 4-4 ofFIG. 3 and showing one of exhaust passages;

FIG. is a rear elevation of the boat assembly unit comprising themounting plate and the tilt housing;

FIG. 6 is a section taken on line 66 of FIG. 1 and showing the steeringand trim mechanism in top plan 5 view with parts broken away andsectioned;

FIG. 7 is a diagram showing the hydraulic circuit for operating thesteering mechanism; and

FIG. 8 is a diagram showing the hydraulic circuit for operating the trimcylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENT The stern drive of the presentinvention. as illustrated in the accompanying drawings, comprises ingeneral a boat mounting assembly and a drive assembly 2.

The boat mounting assembly 1 comprises an outer mounting plate 3 adaptedto be secured to the rear transom 4 of a boat and to be sealedthereagainst to close the opening 5 in the transom.

The engine 6 is mounted inboard of the boat with its transmission 7carried directly by the outer mounting plate 3.

The boat mounting assembly 1 additionally comprises a tilt housing 8which is carried by mounting plate 3 to pivot upon a horizontaltransverse tilt axis 9 by means of trunnions 10 disposed in bearings llofthe mounting plate.

A hydraulically operated trim cylinder I2 is pivotally secured to tilthousing 8 on a transverse axis 13 parallel to tilt axis 9.

The outer end of the piston rod 14 for piston 15 operative in cylinder12 is pivotally secured to mounting plate 3 in a recess thereinextending through transom opening 5 with the pivot 16 disposed inboardof the boat and parallel to tilt axis 9.

The tilt housing 8 carries a hydraulic steering mechanism 17 adapted tobe connected to the dirigible part of the drive assembly 2 for steeringthe latter.

Various hydraulic steering mechanisms 17 may be employed, that shown andpreferred, comprising a pair of cylinders 18 each having a plunger 19and extending rearwardly on opposite sides of the tilt housing 8.

The plungers I9 are secured to the tilt housing 8 by suitable universalball and socket connections 20 each having a retainer plate 21 therefor.

The mounting plate 3 has an opening 22 therethrough for receiving thehorizontal drive shaft 23 extending rearwardly from transmission 7 witha double universal joint 24 therein and with the free rear end of theshaft splined as at 25 for connection to the drive assembly 2.

A bellows 26 surrounds the universal joint 24 with its outer end sealedto the tilt housing 8 and its inner end 5 sealed to mounting plate 3.

A bellows type seal 27 surrounds shaft 23 and is disposed betweenmounting plate 3 and the housing of transmission 7 to protect theuniversal joint 24 from bilge water and compensate for changes in volumewithin bellows 26 upon tilt movement of housing 8.

The transmission 7 is carried by side posts 28 extending upwardly fromthe inwardly projecting portion 29 of mounting plate 3 which surroundsthe recess containing pivot 16.

The exhaust from engine 6 is conducted by suitable conduit 30 toopenings 31 in the mounting plate 3 on either side of the same beneathtrunnions I0 and from which openings 31 of the exhaust is dischargedrearwardly of the boat.

The mounting assembly I described above may be secured to the boat bythe boat manufacturer, and thus shipped as an integral part of the boat.

For this purpose. a removable protective covering, not shown. may besecured over the rear face of the mounting assembly 1 for shipmentpurposes to protect the splined end of shaft 23 and the rear ends ofsteering mechanism 17.

The drive assembly 2 may be shipped as a separate unit to protect thesame from possible damage, and can be readily secured to the mountingassembly I by the dealer or other purchaser without requiring anyadjustments.

The drive assembly 2 comprises the upper gear hous ing 32 and thedirigible unit or lower gear housing 33.

The upper gear housing 32 comprises a casting which encloses the upperbevel gear shaft 34 and which de pends downwardly along the face of thetilt housing 8 with a vertical sleeve 35 for receiving the upper end ofthe vertical drive shaft 36 and an intermediate steering support tube37.

The upper bevel gear shaft 34 is hollow and splined on the inside toreceive the splined end 25 of drive shaft 23 to effect a drivingconnection therebetween and at the same time provide for the necessaryextension when the tilt housing and drive assembly 2 tilt upwardly ontilt axis 9.

The shaft 34 is mounted in tapered roller bearings 38 at the oppositeends thereof with the construction providing for turning the shaft endto end.

A bevel gear 39 has a shank supporting shaft 34 in one of the bearings38, and is splined upon the shaft for assembly purposes.

The bevel gear 39 meshes with a bevel gear 40 on the upper end ofthevertical drive shaft 36 to drive the latter.

The direction of rotation of vertical drive shaft 36 can be changed byturning shaft 34 end to end whereby the beveled gear 39 will engage theopposite side of beveled gear 40, as may be desirable to cancel out theengine torque reaction on the vertical dirigible units when employingdual drives side by side on the same boat. For this purpose the dualdrives will have their dirigible units connected by a cross link 41 tomaintain steering synchronization.

A seal 42 is disposed between the outer end of shaft 34 and the housing32 to prevent leakage of oil from the housing through the open tubularshaft during shipment and also during operation of the drive.

Likewise, a seal 43 is disposed between the inner end of shaft 34 andthe bearing retainer cap 44 secured to housing 32, to prevent leakage ofoil from the housing during shipment and also during operation of thedrive.

A neoprene gasket 45 is disposed between upper gear housing 32 and tilthousing 8 to prevent water from entering the region ofthe universaljoint 24 inside bellows 26.

The vertical drive shaft 36 is splined to bevel gear 40 and supportedtherein by lock nut 46 threaded onto the upper end of the shaft in arecess in the gear.

The bevel gear 40 is supported in housing 32 by the tapered rollerbearing 47 at the upper end of sleeve 35.

The vertical drive shaft 36 is mounted within a sleeve 48 of the lowerdirigible unit 33 by means of a set of straight roller bearings 49 atthe lower end and the tapered roller bearings 50 near the center of theshaft.

The tapered bearings 47 and 50 are opposed to each other in thrust andthe nut 46 determines the prc-load thereof. For this purpose a needlethrust bearing assembly 51 is disposed between a flange 52 on thesteering support tube 37 and the lower end of sleeve 35.

A suitable bellcville spring washer 53 is disposed hencath nut 46 tomaintain the preload of bearings 47 and 50.

The vertical steering support tube 37 is rotatably disposed withinsleeve 35 by means of upper and lower needle bearings 54.

The dirigible unit 33 has an upper face to which the steering housing 55is secured by bolts 56, with steering support tube flange 52 clampedtherebetween.

The lower end of dirigible unit 33 constitutes the lower gear case 57and skeg 58.

The lower gear case 57 contains the propeller drive shaft 59 mounted insuitable tapered roller bearings 60 therein. Shaft 59 extends rearwardlyfrom gear case 57 through the seals 61 and carries the propeller 62 forthe drive.

To complete the propeller drive connection. bevel gear 63 on the lowerend of vertical drive shaft 36 meshes with a bevel gear 64 fixed onpropeller shaft 59.

The shafts 34, 36 and 59, and the bevel gears 39, 40, 63 and 64 alongwith corresponding bearings 38, 47, 49, 50, 60 and the bearings 51 and54 all operate in a closed oil chamber within the upper gear housing 32and the lower gear housing or dirigible unit 33, and which chamber ismaintained filled with oil at all times to a level corresponding to theposition of the axis of shaft 34. For this purpose, a seal 65 surroundssleeve 35 between it and the steering housing 55 to prevent leakage ofoil between the two housings.

The top of upper gear housing 32 has an access opening with a sealedremovable cover 66 therefor generally co-axial with shaft 36 to providefor machining the inside of the housing and for assembly of gear 40 andnut 46 upon the shaft.

The bellows 26 is protected by suitable overlapping of telescopingportions 67 of tilt housings 8 and 68 of mounting plate 3 curvedconcentric to tilt axis 9.

The steering housing 55 has an abutment ring 69 on each side of the unitand through which the corresponding steering cylinders 18 extend. Thetwo power cylinders 18 have the combined function of a single doubleacting power cylinder.

Each cylinder 18 has a spherically shaped ring 70 thereon adapted toabut rearwardly against and into a socket in abutment ring 69 of agenerally complemental spherical segment shape.

Hydraulic pressures are maintained in the cylinders 18 bearing againstthe ends of the corresponding plungers 19 therein to effect a balance offorces maintaining the dirigible unit 33 in any steering position ofrotation on the vertical steering axis which in the illustrationcoincides with the axis of shaft 36.

As shown in FIG. 7, operation of the cylinders 18 is effected by a powersteering assist system comprising a source 71 of pressure fluid anorbitrol helm or valve unit 72 and suitable locking valves 73 and 74.

The pressure fluid source 71 comprises a sump 75. a gear pump 76 drivenby engine 6 and having its inlet connected to the sump. a pressureconduit 77 leading from the pump discharge outlet to locking valve 73,

and a pressure relief valve 78 in conduit 77 and which returns fluidfrom the conduit to the sump when the system is fully pressurized.

The orbitrol unit 72 may he of the type marketed by the Fluid PowerDivision of Eaton Corporation under the trademark Char-Lynn andillustrated generally in Reissue Pat. No. 25.126 granted Feb. 20. 1962and in Reissue Pat. No. 25.291 granted Dec. 4. I962.

Locking valve 73 receives fluid from conduit 77 and transmits it toorbitrol control unit 72 through passage 79 and which unit 72 thenreturns the fluid through passage 80 to valve 73 and from thence to thesump 75 through return conduit 81.

The orbitrol unit 72 is Connected to the locking valve 74 by twoconduits 82 and 83, and locking valve 74 is in turn connected to theleft hand steering cylinder 18 by conduit 84 and to the right handsteering cylinder 18 by conduit 85.

The locking valve 74 comprises a housing having a central longitudinalbore 86 therein with a plug 87 closing each end of the bore.

An axial passage 88 in the inner end of each plug 87 leads to a lateralpassage 89 which is connected to the corresponding conduit 84 or 85.

A spring biased check valve 90 is disposed axially of each plug toeffect closure of the corresponding axial passage 88 therein.

Conduits 82 and 83 connect with the opposite ends of the bore 86 and areisolated by a valve plunger 91 disposed centrally of the bore.

The plunger 91 carries a pilot pin 92 extending axially therefrom andloosely operative in the corresponding passage 88 to unseat the checkvalve 90 therein when the plunger moves in the corresponding directionin response to a pressure differential in conduits 82 and 83.

When the steering wheel 93 is turned to the right, it thus effects anincrease in fluid pressure in line 82 which then actuates plunger 91 tothe left in FIG. 7 and admits pressure fluid through the right handpassage 88 unseating the corresponding check valve 90 and expanding theleft hand or port cylinder 18 to turn unit 33 in a direction steeringthe boat to the right.

At the same time movement of plunger 91 to the left effects unseating ofthe left hand check valve 90 by the corresponding pilot pin 92 therebyallowing the right hand or starboard cylinder 18 to contract and thefluid therein to flow out through conduit 85 and the correspondinglateral passage 89 and axial passage 88 to bore 86 and thence throughconduit 83 to the orbitrol control unit 72.

Conversely rotation of steering wheel 93 to the left effects an increasein fluid pressure in line 83 which then actuates plunger 91 to the rightin FIG. 7 and admits pressure fluid through the left hand passage 88unseating the corresponding check valve 90 and expand ing the right handor starboard cylinder 18 to turn unit 33 in a direction steering theboat to the left.

At the same time movement of plunger 91 to the right effects unseatingof the right hand check valve 90 by corresponding pilot pin 92 therebyallowing the left hand or port cylinder 18 to contract and the fluidtherein to flow out through conduit 84 and the corresponding lateralpassage 89 and axial passage 88 to bore 86 and thence through conduit 82back to the orbitrol control unit 72.

Orbitrol control unit 72 is directly operated by manual turning of thesteering wheel 93 disposed at a convenient place in the boat for theoperator.

Whenever unit 72 is being actuated by steering wheel 5 93. the flow offluid through unit 72 between passages 79 and 80 becomes modified toeffect a pressure differential between conduits 82 and 83.

Whenever steering wheel 93 is stationary, the orbi trol unit 72 tends toblock the flow 0f fluid therethrough between conduits 82 and 83. At thesame time. locking valve 74 is neutralized and locks the fluid in thecorresponding cylinders 18 to thereby prevent turning of unit 33 byexternal forces upon the unit.

In the event ofa failure of pressure in conduit 77. the locking valve 73in effect disconnects orbitrol control unit 72 from the fluid pressuresource 71, and manual steering by turning of wheel 93 is effected bytransfer of pressure fluid between conduits 82 and 83 depending upon thedirection of steering wheel rotation to effect a corresponding expansionand contraction of the port and starboard cylinders 18 and steering ofthe boat.

The locking valve 73 serves to retain the fluid in the orbitrol controlsystem during the manual steering just described. Additionally when thefluid pressure source 71 is operative to supply fluid under pressurethrough locking valve 73 and conduit 79 to the orbitrol unit 72. fluidin the control system is continually replenished to compensate forleakage of fluid from the orbitrol unit back through passage 80 andlocking valve 73.

Referring to FIG. 8, the trim cylinder 12 is connected at its oppositeends by conduits 94 and 95, respectively to a source 96 of power fluid.

The fluid source 96 basically comprises a reversible motor driven gearpump 97 connected to receive hydraulic fluid from a reservoir 98 ineither direction of operation.

For this purpose, passage 99 supplies fluid from reservoir 98 to pump 97when the latter operates in a direction to effect outward and upwardtilt of tilt housing 8, and passage 100 supplies fluid from reservoir 98to pump 97 when the latter operates in a direction to effect downwardand inward movement of tilt housing 8.

Each passage 99 and 100 has a floating ball check valve 101 therein toprevent fluid being discharged by pump 97 from flowing directly to thereservoir 98.

The pump 97 discharges fluid received from passage 99 into the up-lineconduit 94 through a check valve 102 which maintains the pressure in theup-line conduit 94 when the pump 97 is stopped.

The pump 97 discharges fluid received from passage 100 into thedown-line conduit 95 through a check valve 103 which maintains thepressure in the downline conduit 95 when the pump 97 is stopped.

When the up-line conduit 94 is pressurized by pump 97, the cylinderchamber 104 on the front side of the piston becomes pressurized and thepiston is forced outwardly of the cylinder to extend the latter andeffect an upward tilting of the tilt housing 8 and drive assembly 2 ontilt axis 9. At the same time. fluid in cylinder chamber 105 on the backside of piston 15 is forced out through down-line conduit 95 and passage106 to reservoir 98.

The passage [06 has a variable resistant spring biased ball check valve107 which allows fluid to pass at low velocities but checks the flowwhen a predetermined high velocity is reached.

Between valve 107 and reservoir 98, the passage 106 has an adjustablepressure relief check valve 108 for the purpose of maintaining apredetermined pressure on the back side of piston to prevent trail-outand also provide the necessary transfer of thrust of the propellerduring reverse rotation of it.

When the down-line conduit 95 is pressurized by pump 97, the cylinderchamber 105 becomes pressurized to force the piston 15 inwardly of thecylinder 12 thereby contracting the latter and effecting a down wardtilt movement of housing 8 and drive assembly 2 on tilt axis 9. At thesame time, fluid in cylinder chamber 104 is forced out through up-lineconduit 94 and check valve 102 to passage 100 leading to the inlet ofpump 97. For this purpose check valve 102 is forced open by a pilotplunger 109 actuated by fluid pressure from the discharge side of pump97.

An adjustable pressure relief valve 110 by-passcs check valve 101 inpassage 100 to relieve the excess pressure in cylinder chamber 104 atthe end of the piston stroke when the drive assembly 2 has been raisedto its highest tilt position and before pump 97 is stopped.

An adjustable pressure relief valve 111 connects upline conduit 94 toreservoir 98 and is normally set to open at a high pressure to protectthe system from possible external overload forces.

The piston 15 has a plurality of circumferentially spaced spring biasedcheck valves 112 to prevent flow of fluid through the piston fromchamber 104 to chamber 105. and to allow a restricted flow of fluidthrough the piston from chamber 105 to chamber 104 in the event chamber105 becomes excessively pressurized by external forces sufficient tosubstantially close check valve 107.

Lateral forces on the drive assembly 2 are transmitted to the tilthousing 8 and supported by the thrust washers 113 encircling the base ofthe trunnions 10 between the tilt housing 8 and the transom plate 3 atthe upper end of the housing as shown in FIG. 3, and by the verticalside surfaces 114 of connections at the lower end of housing 8 bearingagainst complementary rearwardly extending vertical guide surfaces 115of the transom plate 3 as shown in FIG. 6.

As shown also in FIGv 6, the upper gear housing 32 is constructed toprovide stops 116 disposed on either side to be engaged by thecorresponding steering abutment rings 69 to limit the angulardisplacement of dirigible unit 33 for steering purposes.

In the construction illustrated, the steering or dirigible unit 33 isentirely suspended from upper gear housing 32 by means ofthe verticaldrive shaft 36. Thus, the same bearings generally serve to support theshaft 36 and also the dirigible unit 33. The assembly of the driveassembly 2 is thereby made lighter and more compact, and the assemblyand disassembly thereof is facilitated.

The low mounting of the stern drive on the boat transom and the relativeshort angular tilt movement limited by the dimensions of the trimcylinder 12 and its location relative to tilt axis 9 generally preventsthe propeller 62 from reaching an inoperative position upon upwardtilting of the unit.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

1. A stern drive for boats comprising a boat mounting assembly adaptedto be secured to the transom of a boat and to provide a drive connectionfrom an inboard engine; and a drive assembly removably secured to saidboat mounting assembly and comprising a substantially vertical driveshaft having means connecting the same to said drive connection; anunderwater dirigible unit suspended solely by said drive shaft, apropeller carried by said unit and operatively connected to be driven bysaid shaft, said boat mounting assembly comprising a transom plate and atilt housing pivotally secured to said transom plate on a transverseaxis with adjustable trim and power tilt mechanism therebetween, andsaid drive assembly being rcmovably secured to said tilt housing to tilttherewith. and a double universal joint in said drive connection andsubstantially coincident to said transverse axis.

2. The construction of claim 1 in which said boat mounting assemblycomprises an exhaust discharge passage therethrough adapted to beconnected to receive the exhaust from said inboard engine and todischarge the same rcarwardly of the transom independent of said driveassembly.

3. The construction of claim 1 and hydraulic means connecting saidtransom plate and tilt housing at a predetermined radial distance fromsaid transverse axis to constitute said trim mechanism and control thetrim position of the drive assembly relative to the boat.

4. The construction of claim 3 in which said hydraulic means comprises apower cylinder with a piston therein and means to pressurize saidcylinder on either side of said piston. said last named means providingthe transfer of thrust from said drive assembly to the boat for eitherdirection of drive of the boat without need for mechanical interlocks.

5. The construction of claim 1 in which said boat mounting assemblycomprises a transom plate and a tilt housing pivoted to said transomplate on a horizontal transverse axis; said drive connection comprises agenerally horizontal drive shaft extending through said transom plateand having its outer end disposed to tilt with said tilt housing;universal joint means in said shaft with the center thereof disposednear to said tilt axis, beliows means between said transom plate andsaid tilt housing to enclose said universal joint means and anexpandable bellows type seal between said transom plate and the engineand enclosing the inner end of said drive connection, said seal servingto protect said universal means from bilge water and prevent unduedeformation of said first named bellows.

6. The construction of claim 1 and hydraulic means disposed between saidtilt housing and said dirigible unit to control the steering of saiddirigible unit upon the axis of said drive shaft.

7. The construction of claim 6 in which said hydraulic means comprises asource of fluid pressure, fluid power means disposed to move saiddirigible unit to a predetermined set angular position, and an orbitrolhelm selectively transmitting pressure fluid from said source to saidpower means.

8. The construction of claim 6 in which said hydraulic means comprises adouble acting power cylinder means, and abutment means on said dirigibleunit universally interengaging with said hydraulic means.

9. The construction of claim 8 in which said hydraulic means comprises apower cylinder disposed on each side of said drive assembly, and meansto selectively 9 pressurize said cylinders to effect steering of saiddirigi ble unit.

10. The construction of claim 8 in which said hydrauhe means is carriedby said tilt housing to provide for steering of said dirigible unitindependently of the tilting of said tilt housing.

ll. The construction of claim 9 in which said hydraulic means is carriedby said tilt housing to provide for steering of said dirigible unitindependently of the tilt position of said tilt housing.

12. An outboard stern drive for boats comprising a boat mountingassembly adapted to be secured to the transom of a boat and to provide adrive connection from an inboard engine, said drive connection beingcarried by the engine and comprising a shaft having a splined pilotouter end extending outwardly of the face of said mounting assembly; anda drive assembly carried by said mounting assembly and comprising anupper gear housing, a tubular beveled gear shaft mounted in end bearingsin said housing and disposed to receive the splined pilot end of saidextending shaft substantially in the central region of the tubularshaft, beveled gears connecting said tubular gear shaft and a verticaldrive shaft in said upper gear housing, said housing constituting an oilchamber for running said gears and said bearings in oil, and meansexternal of said bearings and sealing said chamber between said housingand said tubular gear shaft at the opposite ends of the latter to retainthe oil in said chamber.

13. An outboard stern drive for boats, comprising an upper gear housing,a horizontal tubular gear shaft in said housing adapted to be connectedto an inboard engine to drive the same, a vertical drive shaft dependingfrom said housing with said tubular shaft extending across the upper endof said vertical drive shaft, a bevel gear, and bearing means atopposite ends of said tubular shaft in said housing and spaced equallyfrom the axis of said vertical shaft, said tubular shaft being adaptedfor displacement bodily end for-end in said bearing means to disposesaid first named bevel gear selectively on opposite sides of said secondbevel gear to effect reversal in the direction of rotation ofsaidvertical drive shaft.

14. The construction of claim 13 for each of two paired stern drivesdisposed side by side on the same transom, and in which said tubularshaft and the beveled gear thereon for one stern drive is disposed todrive its corresponding vertical drive shaft in a direction opposite tothe drive of the vertical drive shaft for the companion stern drive, adirigible drive unit having an underwater propeller for each stern driveconnected to be driven by the corresponding vertical shaft, and a linkbetween said dirigible units of said stern drives to counteract torquereactions produced by the opposite rotation of said vertical driveshafts.

[5. In a stern drive for boats, an upper gear housing, having adownwardly depending vertical drive shaft and a dirigible lowerpropulsion unit carried by said shaft, said upper gear housing having adepending vertical sleeve, and said propulsion unit having an upwardlyextending steering support tube operatively supported by hearings insaid sleeve. said sleeve and said support tube being generally coaxialwith said vertical drive shaft. a thrust bearing supporting saidvertical drive shaft upon the upper end of said sleeve, a thrust bearingsupporting said steering support tube on a shoulder of said verticaldrive shaft, means to prc-load said thrust hearings in opposition toeach other, and anti-friction bearing means between said dirigible unitand said upper gear housing to accommodate said pre load.

16. In a stern drive for boats having a dirigible propulsion unit andmeans for mounting the same upon the transom of a boat, hydraulicsteering means for said propulsion unit comprising a power cylindermeans disposed on each side of said dirigible unit and carried by saidmounting means, abutment means on said dirigible unit universallyinterengaging with said hydraulic means and means to selectivelypressurize said cylinders to effect steering of said unit,

17. The construction of claim 16 in which said hydraulic steering meanscomprises a source of fluid pressure, and an orbitrol helm selectivelytransmitting pressure fluid from said source to said power cylindermeans.

18. in a stern drive for boats, a drive shaft connected to be driven byan inboard engine and extending rearwardly of the transom with a splinedpilot outer end, an upper gear housing mounted rearwardly of the boattransom, an underwater propulsion unit having a generally vertical driveshaft extending upwardly into said upper gear housing, a tubular bevelgear shaft mounted in bearings in said housing and disposed selectivelyto receive the splined pilot end of said extending shaft therein fromeither end, bevel gears connecting said tubular gear shaft and saidvertical drive shaft in said upper gear housing, said housingconstituting an oil chamber for running said gears in oil, and meanssealing said chamber between said housing and said tubular gear shaft atthe opposite ends of the latter to retain the oil in said chamber.

19. In a stern drive for boats, an upper gear housing adapted to bemounted rearwardly of a boat transom, a drive connection from an inboardengine and having a splined pilot end extending into said gear housing,a tubular gear shaft in said housing disposed to receive said pilot endof said drive connection and to be driven thereby, a generally verticaldrive shaft extending upwardly into said gear housing beneath saidtubular shaft with their axes substantially intersecting, a bevel gearon the upper end of said vertical shaft, a bevel gear on said tubularshaft meshing with said first named bevel gear to drive the latter, andbearing means at opposite ends of said tubular shaft in said housing,said tubular shaft being adapted for displacement bodily end-forend insaid bearing means to dispose said second named bevel gear selectivelyon opposite sides of said first named bevel gear to effect reversal inthe direction of rotation of said vertical drive shaft.

20. The construction of claim 19 and a dirigible lower propulsion unitsuspended from said gear housing and adapted to steer upon a steeringaxis coincident with the axis of said vertical drive shaft.

21. The construction of claim 20 for each of two paired stern drivesdisposed side by side on the same transom, and in which said tubularshaft and the beveled gear thereon for one stern drive is disposed todrive its corresponding vertical drive shaft in a direction opposite tothe drive of the vertical drive shaft for the companion stern drive, anda link between said dirigible units of said stern drives to counteracttorque reactions produced by the rotation of said vertical drive shafts.

22. In a stern drive for boats, 21 transom plate, a tilt housing pivotedto said transom plate on a horizontal transverse axis. a driveconnection comprising a generally horizontal drive shaft extending froman inboard engine freely through said transom plate and having its outerend disposed to tilt with said tilt housing, universal joint means insaid shaft with the center thereof disposed near to said tilt axis,bellows means between said transom plate and said tilt housing toenclose said universal joint means, and an expandable bellows type sealbetween said transom plate and the engine and enclosing the inner end ofsaid drive connection. said seal serving to protect said universal meansfrom bilge water and prevent undue deformation of said first namedbellows.

23. In a stern drive for boats mounting means adapted to be secured tothe transom ofa boat and having a tilt housing pivotally carried therebyon a transverse horizontal tilt axis, a dirigible propulsion unitsuspended from said tilt housing to turn on a substantially verticalsteering axis, and hydraulic steering means for said propulsion unitcomprising a power cylinder on each side of said unit and carried bysaid tilt housing, abutment means on said dirigible unit engaged by saidpower cylinders, and means to selectively pressurize said powercylinders to effect steering movement of said propulsion unitindependently of the tilt position of said tilt housing.

1. A stern drive for boats comprising a boat mounting assembly adaptedto be secured to the transom of a boat and to provide a drive connectionfrom an inboard engine; and a drive assembly removably secured to saidboat mounting assembly and comprising a substantially vertical driveshaft having means connecting the same to said drive connection; anunderwater dirigible unit suspended solely by said drive shaft, apropeller carried by said unit and operatively connected to be driven bysaid shaft, said boat mounting assembly comprising a transom plate and atilt housing pivotally secured to said transom plate on a transverseaxis with adjustable trim and power tilt mechanism therebetween, andsaid drive assembly being removably secured to said tilt housing to tilttherewith, and a double universal joint in said drive connection andsubstantially coincident to said transverse axis.
 2. The construction ofclaim 1 in which said boat mounting assembly comprises an exhaustdischarge passage therethrough adapted to be connected to receive theexhaust from said inboard engine and to discharge the same rearwardly ofthe transom independent of said drive assembly.
 3. The construction ofclaim 1 and hydraulic means connecting said transom plate and tilthousing at a predetermined radial distance from said transverse axis toconstitute said trim mechanism and control the trim position of thedrive assembly relative to the boat.
 4. The construction of claim 3 inwhich said hydraulic means comprises a power cylinder with a pistontherein and means to pressurize said cylinder on either side of saidpiston, said last named means providing the transfer of thrust from saiddrive assembly to the boat for either direction of drive of the boatwithout need for mechanical interlocks.
 5. The construction of claim 1in which said boat mounting assembly comprises a transom plate and atilt housing pivoted to said transom plate on a horizontal transverseaxis; said drive connection comprises a generally horizontal drive shaftextending through said transom plate and having its outer end disposedto tilt with said tilt housing; universal joint means in said shaft withthe center thereof disposed near to said tilt axis, bellows meansbetween said transom plate and said tilt housing to enclose saiduniversal joint means and an expandable bellows type seal between saidtransom plate and the engine and enclosing the inner end of said driveconnection, said seal serving to protect said universal means from bilgewater and prevent undue deformation of said first named bellows.
 6. Theconstruction of claim 1 and hydraulic means disposed between said tilthousing and said dirigible unit to control the steering of saiddirigible unit upon the axis of said drive shaft.
 7. The construction ofclaim 6 in which said hydraulic means comprises a source of fluidpressure, fluid power means disposed to move said dirigible unit to apredetermined set angular position, and an orbitrol helm selectivelytransmitting pressure fluid from said source to said power means.
 8. Theconstruction of claim 6 in which said hydraulic means comprises a doubleacting power cylinder means, and abutment means on said dirigible unituniversally interengaging with said hydraulic means.
 9. The constructionof claim 8 in which said hydraulic means comprises a power cylinderdisposed on each side of said drive assembly, and means to selectivelypressurize said cylinders to effect steering of said dirigible unit. 10.The construction of claim 8 in which said hydraulic means is carRied bysaid tilt housing to provide for steering of said dirigible unitindependently of the tilting of said tilt housing.
 11. The constructionof claim 9 in which said hydraulic means is carried by said tilt housingto provide for steering of said dirigible unit independently of the tiltposition of said tilt housing.
 12. An outboard stern drive for boatscomprising a boat mounting assembly adapted to be secured to the transomof a boat and to provide a drive connection from an inboard engine, saiddrive connection being carried by the engine and comprising a shafthaving a splined pilot outer end extending outwardly of the face of saidmounting assembly; and a drive assembly carried by said mountingassembly and comprising an upper gear housing, a tubular beveled gearshaft mounted in end bearings in said housing and disposed to receivethe splined pilot end of said extending shaft substantially in thecentral region of the tubular shaft, beveled gears connecting saidtubular gear shaft and a vertical drive shaft in said upper gearhousing, said housing constituting an oil chamber for running said gearsand said bearings in oil, and means external of said bearings andsealing said chamber between said housing and said tubular gear shaft atthe opposite ends of the latter to retain the oil in said chamber. 13.An outboard stern drive for boats, comprising an upper gear housing, ahorizontal tubular gear shaft in said housing adapted to be connected toan inboard engine to drive the same, a vertical drive shaft dependingfrom said housing with said tubular shaft extending across the upper endof said vertical drive shaft, a bevel gear, and bearing means atopposite ends of said tubular shaft in said housing and spaced equallyfrom the axis of said vertical shaft, said tubular shaft being adaptedfor displacement bodily end-for-end in said bearing means to disposesaid first named bevel gear selectively on opposite sides of said secondbevel gear to effect reversal in the direction of rotation of saidvertical drive shaft.
 14. The construction of claim 13 for each of twopaired stern drives disposed side by side on the same transom, and inwhich said tubular shaft and the beveled gear thereon for one sterndrive is disposed to drive its corresponding vertical drive shaft in adirection opposite to the drive of the vertical drive shaft for thecompanion stern drive, a dirigible drive unit having an underwaterpropeller for each stern drive connected to be driven by thecorresponding vertical shaft, and a link between said dirigible units ofsaid stern drives to counteract torque reactions produced by theopposite rotation of said vertical drive shafts.
 15. In a stern drivefor boats, an upper gear housing, having a downwardly depending verticaldrive shaft and a dirigible lower propulsion unit carried by said shaft,said upper gear housing having a depending vertical sleeve, and saidpropulsion unit having an upwardly extending steering support tubeoperatively supported by bearings in said sleeve, said sleeve and saidsupport tube being generally coaxial with said vertical drive shaft, athrust bearing supporting said vertical drive shaft upon the upper endof said sleeve, a thrust bearing supporting said steering support tubeon a shoulder of said vertical drive shaft, means to pre-load saidthrust bearings in opposition to each other, and anti-friction bearingmeans between said dirigible unit and said upper gear housing toaccommodate said pre-load.
 16. In a stern drive for boats having adirigible propulsion unit and means for mounting the same upon thetransom of a boat, hydraulic steering means for said propulsion unitcomprising a power cylinder means disposed on each side of saiddirigible unit and carried by said mounting means, abutment means onsaid dirigible unit universally interengaging with said hydraulic meansand means to selectively pressurize said cylinders to effect steering ofsaid unit.
 17. The construction of claim 16 in which said hydraulicsteering means comprises a source of fluid pressure, and an orbitrolhelm selectively transmitting pressure fluid from said source to saidpower cylinder means.
 18. In a stern drive for boats, a drive shaftconnected to be driven by an inboard engine and extending rearwardly ofthe transom with a splined pilot outer end, an upper gear housingmounted rearwardly of the boat transom, an underwater propulsion unithaving a generally vertical drive shaft extending upwardly into saidupper gear housing, a tubular bevel gear shaft mounted in bearings insaid housing and disposed selectively to receive the splined pilot endof said extending shaft therein from either end, bevel gears connectingsaid tubular gear shaft and said vertical drive shaft in said upper gearhousing, said housing constituting an oil chamber for running said gearsin oil, and means sealing said chamber between said housing and saidtubular gear shaft at the opposite ends of the latter to retain the oilin said chamber.
 19. In a stern drive for boats, an upper gear housingadapted to be mounted rearwardly of a boat transom, a drive connectionfrom an inboard engine and having a splined pilot end extending intosaid gear housing, a tubular gear shaft in said housing disposed toreceive said pilot end of said drive connection and to be driventhereby, a generally vertical drive shaft extending upwardly into saidgear housing beneath said tubular shaft with their axes substantiallyintersecting, a bevel gear on the upper end of said vertical shaft, abevel gear on said tubular shaft meshing with said first named bevelgear to drive the latter, and bearing means at opposite ends of saidtubular shaft in said housing, said tubular shaft being adapted fordisplacement bodily end-for-end in said bearing means to dispose saidsecond named bevel gear selectively on opposite sides of said firstnamed bevel gear to effect reversal in the direction of rotation of saidvertical drive shaft.
 20. The construction of claim 19 and a dirigiblelower propulsion unit suspended from said gear housing and adapted tosteer upon a steering axis coincident with the axis of said verticaldrive shaft.
 21. The construction of claim 20 for each of two pairedstern drives disposed side by side on the same transom, and in whichsaid tubular shaft and the beveled gear thereon for one stern drive isdisposed to drive its corresponding vertical drive shaft in a directionopposite to the drive of the vertical drive shaft for the companionstern drive, and a link between said dirigible units of said sterndrives to counteract torque reactions produced by the rotation of saidvertical drive shafts.
 22. In a stern drive for boats, a transom plate,a tilt housing pivoted to said transom plate on a horizontal transverseaxis, a drive connection comprising a generally horizontal drive shaftextending from an inboard engine freely through said transom plate andhaving its outer end disposed to tilt with said tilt housing, universaljoint means in said shaft with the center thereof disposed near to saidtilt axis, bellows means between said transom plate and said tilthousing to enclose said universal joint means, and an expandable bellowstype seal between said transom plate and the engine and enclosing theinner end of said drive connection, said seal serving to protect saiduniversal means from bilge water and prevent undue deformation of saidfirst named bellows.
 23. In a stern drive for boats, mounting meansadapted to be secured to the transom of a boat and having a tilt housingpivotally carried thereby on a transverse horizontal tilt axis, adirigible propulsion unit suspended from said tilt housing to turn on asubstantially vertical steering axis, and hydraulic steering means forsaid propulsion unit comprising a power cylinder on each side of saidunit and carried by said tilt housing, abutment means on said dirigibleunit engaged by said power cylinders, and means to selectivelypressurize said power cylInders to effect steering movement of saidpropulsion unit independently of the tilt position of said tilt housing.